Horror with a message

Normally I'm not a fan of horror movies, or of preachy films with heavy-handed social or environmental messages.

But I was still drawn in by two movies my husband, a film buff, was watching at home last week — "The Happening," released in 2008, and "District 9," released in 2009. Both are available on DVD.

In "The Happening," Mark Wahlberg stars as a slightly nerdy science teacher who is shocked when people on the East Coast begin to kill themselves in grisly ways. At first, everyone thinks the deaths are caused by terrorists who have released a neurotoxin that reverses a person's instinct for self-preservation.

With the help of a botanist, Wahlberg realizes plants are releasing the neurotoxins as a defense mechanism against humans, who are destroying the environment.

Sounds far-fetched, right? But scientists tell us that plants and trees actually do release airborne chemicals to defend themselves and warn other vegetation of impending danger.

According to research reported in Discover magazine, when a caterpillar eats a tobacco leaf, the plant recognizes compounds in the insect's saliva and produces toxins to kill it. The tobacco plant also releases chemicals that attract parasitic wasps that lay eggs on caterpillars. The wasp larvae feed on the live caterpillars and eventually kill them. Many other plants and trees employ similar strategies.

In hopes of reducing pesticide use, researchers are already tinkering with ways to get crops to ramp up their natural production of defensive chemicals. We could become the victims of the chemicals if things went disastrously wrong.

In "District 9," a massive alien spaceship coasts to a stop in the sky above Johannesburg, South Africa. When humans look inside, they find emaciated aliens living in filth. The aliens' ship is out of fuel, and the stranded creatures are settled near Johannesburg in District 9, which degenerates into a squalid, violent refugee camp.

The sense of fear and danger rises as we see how the insect-like aliens are so much stronger than humans. They gorge on animal carcasses and fight over canned cat food. The aliens are also developing sophisticated weapons that are biologically engineered so that they can only be used by aliens. It's easy to get the feeling that the humans in the film should exterminate the aliens — the sooner, the better.

Bumbling bureaucrat Wikus van de Merwe, played by Sharlto Copley, arrives on the scene to serve eviction papers to the aliens as humans attempt to remove the creatures from District 9 and resettle them far from Johannesburg or any other city. Van de Merwe knows their language and many of their customs and tastes, and tries to keep his armed military escort under control during tense standoffs with the aliens, who don't want to leave their homes. But he's still enthusiastic when his men use flamethrowers to destroy alien eggs and babies.

Before long, the line separating the civilized humans from the violent aliens blurs and disappears. Van de Merwe is forced by desperate circumstances into befriending an alien, who has a loving bond with his alien child. He finds out that humans are performing torturous experiments as they try to find ways to use the aliens' potentially valuable weapons.

Viewers who thought in the beginning of the movie that all the aliens should be killed in order to protect humanity will eventually be squirming in their chairs.